Air-to-ground and air-to-air radio communications are important to safe aircraft flight. Modern aircraft are equipped with a multitude of radio communications systems, many of them operating in generally the same Very High Frequency (VHF) radio band (30 MHz to 300 MHz). These various radio systems allow the aircraft to remain in essentially constant communication with the ground. Flight crews use so-called “comm” voice radios to talk with air traffic controllers to get clearance to take off, land, change altitude and/or course, and for other reasons. The flight crews also use voice radios to exchange important safety information with other nearby aircraft. Such simplex or half-duplex VHF radio transceivers mute or inhibit a radio receiver while an associated transmitter is operating. Most modern radio transceivers operate in this fashion (i.e., the receiver circuitry within the transceiver is disabled whenever the user depresses PTT (push to talk) to activate the transmitter).
VHF radio communications is also used to carry data to and from the aircraft. Such data communications can give pilots updated weather and other alert information and can also automatically inform ground crews about the status of the aircraft's vital systems.
Most commercial aircraft are currently equipped with three VHF Radios, two of which are used for ATC voice communications and one is used for ACARS data link, also referred to Airlines Operational Control (AOC) communications. Generally speaking, only one radio is used for data communications because the type of data communications is not considered essential for the dispatch of the aircraft. These various different radios supply redundancy in case of failure and also provide compatibility with different communications systems and networks.
The most prevalent data radio communications system in current commercial aircraft use is ACARS (Aircraft Communication Addressing and Reporting System), a two-way VHF data link messaging system primarily utilized by air carriers. This system has been successfully used for routine AOC and AAC text messages, such as weather, dispatch, and administrative messages. Such messages for example can be displayed on an ACARS CRT or other display in the aircraft cockpit. ACARS has also been demonstrated for certain ground and in-flight messages, such as pre-departure clearances, expected taxi clearances, and Digital Automatic Terminal Information Service (D-ATIS). This experience has shown the potential for data link as a responsible use of spectrum resources and support for enhanced flightcrew situational awareness. See for example ARINC 607 and FAA Advisory Circular No. 00-63 (Sep. 24, 2004), each incorporated herein by reference.
The ACARS system components on board an aircraft can receive data from the ground and can send data upon flight crew command. The ACARS system is also designed to send data messages automatically and autonomously to ground based stations with no requirement for flight crew interaction. A network of VHF ground based transceivers (often referred to as Remote Ground Stations, or RGSs) provide typical ranges that are dependent on altitude, with a 200-mile transmission range common at high altitudes. This network of ground stations can receive ACARS data transmissions from the aircraft and forward them to appropriate ground resources (e.g., an airline's maintenance personnel). For example, the ACARS system can automatically transmit engine data concerning engine status or problems (e.g., excessive engine vibration or oil temperature). Such transmissions can be initiated without any flight crew action, and enable ground personnel to be notified of potential problems on the aircraft in real time.
One problem encountered in the past relates to interference between other on-board co-band or other radios. Because the flight crew does not control when an ACARS transceiver begins to autonomously transmit VHF data bursts, it sometimes happens (as FIG. 1 illustrates) that the flight crew may be trying to receive and listen to VHF voice transmissions on a different VHF frequency (e.g., from a control tower, an air traffic controller, or another airplane) at the same time the ACARS system begins transmitting. The autonomously-initiated ACARS VHF transmissions can cause interference to other active onboard receivers operating on the same (e.g., VHF) radio band. For example, when ACARS begins transmitting a data burst, a voice communications radio in the process of receiving a tower or other voice communication may produce a chirp noise. Such chirp noise “interference” can significantly disrupt the operation of the other active VHF transceivers in the vicinity and cause problems with intelligibility.
Flight crews sometimes complain that the ACARS data burst interrupts communications with the tower upon departure, and they have to ask the tower to repeat instructions to them. Therefore, there is some concern on the flight crew's part in being able to maintain communications. See for example ARINC Report Reference 05-105/MSG-211 entitled “Communications Systems” item no. 72 at page 78 of Avionics Maintenance Conference 2005 AMC Report (Apr. 25-28, 2005 Atlanta Georgia).
There have been past efforts to minimize such interference. Some past approaches have used traditional processes involving antenna separation. Increasing the physical distance between antennas mounted on the aircraft fuselage can reduce the potential for interference. Antennas mounted on the same side of the aircraft are generally provided at a minimum separation (e.g., 38 feet) to achieve necessary isolation. However, size limitations on business and regional aircraft can preclude installing the antennas with spacing adequate to provide 40 dB of isolation necessary to prevent cross talk.
Other approaches have relied on activation of a so-called “Simulcom” feature on certain VHF radios that promotes gain reduction in reception mode. Given the limitation of antenna spacing and therefore the operating environment, activation of the Simulcom feature on certain VHF radios provides some improvement by reducing receiver gain when another radio is keyed. However, Simulcom may not eliminate cross talk in all cases. For specific problems of ACARS interference at take off, some radio manufacturers suggest delaying transmission of the ACARS “OFF” event a certain wait time (e.g., 20 seconds to approximately 90 seconds) after the weight off wheels transition. See e.g., ARINC Reference 05-105/MSG-2W cited above. This could minimize any interference during critical communications with ATC but has its own set of issues.
While much work has been done in the past, further improvements are possible and desirable.
The exemplary illustrative non-limiting technology described herein includes an electronic circuit that monitors the incoming voice or other information content on plural VHF radio receivers or transceivers, and selectively inhibits any transmission on the third VHF with the associated ACARS. The exemplary illustrative non-limiting intervention causes no penalty since the ACARS data terminal will retry transmission of the data as soon the associated VHF has been reestablished
The proposed exemplary illustrative non-limiting technology herein can for example be incorporated as a feature on ACARS equipment.